Crank Trigger Error

Hey guys, hopefully someone can help me out with this issue.

My Application:

• Honda RC51 90° V-Twin (motorcycle)

• FuelTech FT550

• Coil-on-plug setup

• Trigger Wheel: 12-1

• Cam Sync Wheel: 3-tooth

• Cam & Crank Sensors: VR

Background:

The OEM crank trigger wheel is a 12-tooth (no missing tooth) setup, and the cam has three teeth—one at 180° AFTD, another 180° from that, and a third 30° after the second. I was getting solid signals and confirmed correct polarity using the oscilloscope function.

However, I was having trouble getting CAM sync. I reached out to FuelTech, and they said the ECU isn’t compatible with this trigger setup. They recommended switching to a 12-1 crank wheel paired with a multi-tooth cam. So, I went ahead and cut one tooth off the crank wheel.

Current Issue:

Now with the modified 12-1 crank wheel, I’m having trouble getting the ECU to pick up sync or detect the missing tooth. I’m getting the following errors:

1. Crank Trigger Error: Gap detected at wrong spot

2. Crank Trigger Error: Missed tooth reading

Still getting the same result. Same errors. For reference, I’m only checking the configuration—I’m not trying to start the engine. Injectors and fuel pump are unplugged.

Scope Observations:

I attached an oscilloscope image of the 12-1 wheel signal, and I can’t see the gap in the log that should represent the missing tooth. I feel like it should be obvious, but I’ve got fresh eyes when it comes to this stuff.

Also, I’m seeing weird voltage spikes in the scope log (I’ve marked them with arrows). Sometimes they’re negative, but mostly positive. They never cross zero or resemble a tooth signal. I didn’t see these spikes with the unmodified trigger wheel. Noise?

Side note: these voltage readings for the crank teeth seem high for 250–350 RPM, right? I’ve seen readings over 20V just cranking on the starter. Maybe just a characteristic of this sensor.

I also attached images of the crank wheel showing where I removed the tooth and the size of the other teeth. I didn’t fully grind the removed tooth down—there’s still a slight smooth hump where the tooth was. Not sure if that hump needs to be completely flush with the rest of the wheel (same diameter as the non-tooth section).

I don’t think it’s interference—the coils aren’t firing since there’s no sync. The crank sensor leads are only close to the starter power cable coming from the relay. But again, I didn’t see this issue before modifying the flywheel. And even when I isolate the leads from the starter cable, the issue still shows up.

Final Thoughts:

Any help would be appreciated. Maybe it’s something as simple as going back to the original crank wheel (12, no missing tooth – I have an extra) and cutting off the extra cam teeth. Or maybe I’ve got something misconfigured in the ECU. The sensor worked fine before I installed the FT550, so I doubt it’s the sensor itself.

(note: The two scope images are from two different logs, one with the arrows is from a plot in excel)

I don't have any experience with the FuelTech ECU, but I wonder since the CAM signal seems to be shifted by 2.5v, if you perhaps have it configured as a Hall sensor and thus a pullup resistor is active. I wold expect that signal (which looks like a VR or Magnetic type sensor) to be centered around 0v.

Are the spark plugs installed? Engine speed variation (unless the battery is very fresh) due to compression can make it very difficult to pick up missing teeth especially when you only have 12 of them. So for initial setup purposes consider removing the spark plugs to make the missing tooth more obvious.

it may be that because the missing tooth is near the compression stroke of one of the cylinders, it can't be detected. Ideally it would occur something like 90 degrees from a compression stroke, where the engine should be turning fast.

Thanks for the response, David.

I pulled the spark plugs and scoped the triggers again. You can clearly see the missing tooth now. Also, the previous scope from my last log was when I wasn’t running sequential, so I had the cam sensor set to ‘not used.’ FuelTech must still log that input and apply the pull-up with that configuration, which is why the cam signal was shifted up. I updated the map and set the cam sensor to the correct configuration, and now the cam signal is centered around 0V. (The new scope image was still with the cam sensor set to ‘not used,’ so again, it’s shifted up.)

I’ve got the tooth removed between the 110° and 50° BTDC teeth, so the missing tooth lands somewhere around 80° BTDC. I’m assuming that’s the issue? Could this just be a characteristic of the starter and battery size (which was fully charged)? This is only a 2-cylinder engine, but what would a higher cylinder count engine do with a 12-tooth crank? Maybe that’s why the OEM went with no missing tooth and used the cam for sync instead. Maybe the battery size just doesn't have enough juice to turn the engine over consistent enough through the compression strokes.

Anyway, I’m able to get sync in both non-sequential and sequential modes with the cam sensor. I still occasionally get the same trigger errors, but at least it’s syncing sometimes. So now it comes down to making sure the ECU reliably sees the missing tooth. Options are: move the crank trigger (not easy in this setup), or switch to a 12-tooth crank with no missing tooth and a single-tooth cam.

Open to any suggestions.

Attachments:

1 - Crank Log (V2): (non-seq) chart from excel - crank only

2 - OscilloscopeData: (non-seq) (same log as attach 1 but from the FTManager) - Crank and Cam

3 - ScopeData(seq): Sequential scope log from FTManager